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Chapter 24: Human Microbiome (Gastrointestinal (Large Intestines (Products…
Chapter 24: Human Microbiome
\(10^{13}\) microorganisms
Composition is very different from human to human
Gastrointestinal
Home to ~\(10^{13}\) microbials
Stomach
Low pH prevents overgrowth
H. pylori
When present, accounts for majority of stomach biomass
Causes chronic inflammation
Carcinogenic
Ulcers
Small intestines
Competes with host for uptake of nutrients
Become anoxic the farther in
Large Intestines
Bacteria
Facultative aerobes
Render colon anoxic
Obligate anaerobes
99% gram-positive
\(1/3\) of weight of fecal matter
\(10^{13}\) cells lost per day
Similar to continuous culture system
Archaea
0.05 - 1%
Goblet cells
Produce mucin
Microbials do not colonize where mucin is present
Produce anti-microbial peptides that protect epithelium
Products
Gas production
\(CO_2\)
\(H_2\)
\(CH_4\)
Vitamin synthesis
\(B_{12}\)
K
Steroid metabolism
Amino acid synthesis
Asparagine
Glutamate
Methionine
Tryptophan
Lysine
Odor production
\(H_2S\)
\(NH_3\)
Organic acid production
Glycosidase reactions
Probiotics
Bacteria that confer health benefit to host
Take up space or nutrients
Limits pathogen colonization
Prebiotics
Carbohydrates that are indigestible by humans
Provide nutrition to fermentative bacteria
Airway
Oral cavity
Saliva
Contains some microbials
Contains antibacterial substances
lysozyme
Causes lysis of of bacteria
lactoperoxidase
Generates toxic form of oxygen
More common microbiome between humans than gut
Keep pathogenic bacteria in check
Disorders
Dental plaque
Fermenting bacteria produce acid that wears down tooth enamel
Periodontal disease
Contributes to cardiovascular disease and arthritis
Respiratory tract
Upper
Microbials thrive
Some healthy people carry pathogens
Pathogens restricted by other microbials
Immune system
Lower
No resident microbiota
Cilia push bacteria back towards upper airway
Urogenital Tract
Kidney
Sterile
Bladder
Sterile
Distal urethra
Colonized by aerobic gram-negative bacteria
Can cause disease if pH or other conditions change
Urinary tract infections
Skin
\(10^{10}\)
Various microenvironments exist
Dry skin
Moist skin
Sebaceous skin
Each microenvironment has its own microbiota